As for the attempt at the above, nearly 40 years ago, it has been reported that an aliphatic polycarbonate (APC) can be obtained through alternating copolymerization of carbon dioxide and epoxide in the presence of a catalyst (see, Non-Patent Documents 1, 2).
Reaction scheme (1) is represented by the following formula:

The above APC is, as shown in the reaction scheme (1), characterized in that it takes carbon dioxide (CO2) in the polymer backbone structure.
According to the reaction scheme, a wide variety of aliphatic polycarbonates (APC) can be produced by variously selecting the polymerization catalyst and by selecting the type of the epoxide. At first, the catalyst was a diethylzinc-water system; however, zinc-based different systems and a wide variety of catalyst systems containing any other metal have become investigated, and still at present, searches for catalyst systems having a higher activity are continuing.
With the recent upsurge in concerns about global warming, the aliphatic polycarbonate (APC) has entered the limelight. In case where this can be widely utilized as a plastic material in industry, then there would be an extremely high possibility for it to be the dominant technology of CO2 fixation.
At present, as a measure against global warming, CO2 reduction is claimed for in the world, and at the present time for CO2 fixation, a technology of capturing it in the depths of the ground or in deep waters is found to be useful for CO2 fixation. However, even in Japan alone, the amount of CO2 emissions from power stations and steel plants is over 500,000,000 tons a year, and construction of CO2 fixation technology is urgently needed, for which the above-mentioned reaction is noteworthy as one measure.
It is said that, in China, test production of poly(propylene carbonate) (PPC) shown by the following reaction scheme 2 has been tried by defining the epoxide in the reaction scheme 1 to an inexpensive monomer, propylene oxide for advanced industrialization of aliphatic polycarbonates (APC).

For PPC in China shown by the above reaction scheme 2, plant production has also been tried with a catalyst system differing from the diethylzinc-water (Et2Zn—H2O) system.
The molecular weight of relatively high-quality PPC produced in such pilot plants is already on a technological level of more than 100,000, and the weight-average molecular weight (Mw) thereof is more than 400,000.
However, at the moment, the glass transition temperature (Tg) of PPC is around 30° C., and the property thereof is soft and rubbery plastic. In addition, its heat resistance is extremely poor, and it readily decomposes at around 200° C. Specifically, as for the mechanical properties thereof, it may be said that PPC has an extremely low elastic modulus and is excellent in elongation at break. The properties are similar to those of adhesive. For example, when once shaped in pellets after production of PPC but while stored as piled up, a phenomenon will occur that the pellets will soon adhere to each other and could not be separated. Having the properties, for example, in case of PPC is formed into a wrapping film; the films will stick together and could be separated with difficulty into the original individual films, after piling the films together for a while. Many properties of PPC that have been heretofore known often serve as impediments to practical use thereof, and it is necessary to improve the properties.
In case where a technology of modifying the current properties of PPC could be developed, then creation of some novel materials could be expected via PPC.
Under the technical background as above, some researches to compounding PPC with various resins so as to elevate as much as possible the glass transition temperature of PPC thereby increasing the heat resistance thereof and improving the mechanical properties thereof are being made.
For example, there is an invention of a material capable of being used as a working binder or a foaming agent for ceramics or metal powders, in which PPC is melt-kneaded with polymethyl methacrylate (PMMA) in different compositions to thereby make the decomposition temperature of the blend material shifted to a high-temperature side by increasing the PMMA ratio therein (see, Patent Document 1).
As in Non-Patent Document 3, a blend is produced by melt-kneading PPC with ethylene-vinyl alcohol copolymer (EVOH), thereby improving the mechanical properties thereof and increasing the thermal decomposition temperature thereof.
Also there is an invention of melt-kneading PPC with polyvinyl acetate (PVAc) in different compositions to thereby improve the mechanical properties of the blend material (see, Patent Document 2).
In Non-Patent Document 4, first a filler (montmorillonite) is dissolved in a benzene solution, then PPC is added to the solution and stirred for a few hours thereby to intercalate PPC in the layer of montmorillonite, and thereafter the solvent is removed to form a film.
Improving the mechanical properties is the principal purpose, but contrary to expectations, the result is that the elastic modulus increased merely by around 2 times or so.
The conventional cases are investigated, and the results in Patent Document 1, Patent Document 2 and Non-Patent Document 3 are as follows: In case where PPC is blended with a resin according to a melt-kneading method, but when the resin is not incorporated in an amount of more than 50% by weight of PPC, then the PPC blend could not exhibit mechanical properties comparable to or better than those of low-density polyethylene that is a typical one of general-purpose resins.
Although for improving the properties of PPC, it is not desirable to reduce the PPC ratio to 50% by weight or less in compounding it with any other resin, for attaining the original purpose intended to fixation technology. Specifically, 43% by weight of CO2 is fixed in the main chain of PPC. In case where compounding PPC with any other resin in an amount of at least 50% by weight is needed, then the result is that the weight ratio of CO2 in the total blend would reduce to at most 20% and the CO2 reducing effect would be seriously impaired, therefore not providing an appealing technology. As in Non-Patent Document 4, the “solution method” using an organic solvent is hardly applicable to a bulk material, and could not be said to be a process suitable for industrialization.
Given the technical background as above and principally aiming to improve PPC, especially to improve the mechanical properties and the heat resistance thereof, we the present inventors have concentrated our efforts on compounding PPC with any other resin according to a melt-kneading method while reducing the blend ratio to at most 50% by weight and further making the resulting blend material exhibit mechanical properties comparable to or better than those of low-density polyethylene, polypropylene and the like that are typical ones of general-purpose resins.